1. Field of the Invention
The present invention relates to a modified chlorinated polypropylene, process for producing the same and use thereof. More particularly, the present invention provides a modified chlorinated polypropylene which is useful as a binder resin that may be contained in a coating composition for various kinds of plastic film, sheet or other synthetic resin products such as, for example, printing inks, paints and adhesives.
2. Description of the Prior Art
As a result of the recent trend toward greater diversification in the field of packagings or containers and improvements in the functional efficacy of synthetic resin products such as synthetic leather, there has recently been a demand for coating compositions with a high level of performance and quality, for example, printing inks, adhesives and various kinds of paints which are employed for decoration, bonding or surface protection on plastic films, plastic sheets or other synthetic resin molded products.
In particular, printing inks which are used to decorate packagings or containers and improve the quality thereof are required to have versatile adhesion properties with respect to various kinds of composite film. These inks are further required to have properties capable of facilitating the various kinds of processing that are undertaken in after-treatments, for example, suitability for the processing that is carried out in a variety of laminating processes (hereinafter referred to as "suitability for lamination"), as well as the ability to withstand boiling and to be used in retort applications.
In general, printing on plastic films or the like is carried out by gravure, flexography or another similar method. However, When films used as packaging materials are printed, web-fed printing is in many cases carried out and the inks which are used for such printing thus need to have quick-drying properties. In cases where plastic films with ink printing applied thereto are used to packages for food, it is particularly important that the amount of residual solvent be minimized.
Packaging materials are often subjected to dry lamination or extrusion lamination processes after printing for the purpose of improving the performance thereof. In particular, polyester (PET), nylon (NY) or other similar films, which are superior to other kinds of film in strength and airtightness, may be laminated with polyethylenes, polypropylene and the like. In such cases, a urethane adhesive or the like is used for dry lamination, while an anchor coat material is used in the case of extrusion lamination. Aluminum foil may be interposed between the individual laminated films to obtain a packaging material which is suitable for both boiling and retort applications. On the other hand, in the field of ordinary packaging materials where a retort strength is not demanded but a transparent base material is used to form a base, it is also common practice to carry out a laminating process wherein oriented polypropylene (OPP) is employed as a base film and this film is directly covered with molten polypropylene without using an anchor coat material (generally known as "PP direct lamination").
In order to carry out post-processing as described above, the printing inks which are employed in the previous steps need to have not only versatile adhesion properties and suitability for printing on a variety of base films but must also be suitable for the processes which take place in the respective post-processing operations. These properties are mainly determined by the binder resins which are used in the printing inks.
Hitherto, printing inks containing a thermoplastic polyester resin as a binder have been employed for printing on polyester films, and two-pot type inks consisting of a polyester resin having a hydroxyl group and an isocyanate compound have been used for nylon and polyester films. Recently, printing inks containing a polyurethane resin as a binder have been used as inks which display a versatile range of properties with respect to nylon, polyester and other base films.
On the other hand, printing inks which contain a chlorinated polyolefin having a relatively low degree of chlorination, for example, chlorinated polypropylene, are used for polyolefin films subjected to PP direct lamination.
The above-described conventional printing inks suffer, however, from the following problems. The inks that employ a thermoplastic polyester resin as a binder can only be applied to a limited range of base films and have unsatisfactory drying properties. Consequently they suffer from problems in terms of workability and are subject to, for example, the occurrence of blocking. The two-pot type inks which are of the reaction type have a disadvantageously short pot-life and are therefore subject to various restrictions on the range of potential working conditions and also to the economic losses that are incurred when ink which has not yet been used but has been chemically changed has to be discarded. The printing inks that employ a polyurethane resin as a binder exhibit satisfactory adhesion to nylon, polyester and other similar films but still often insufficient adhesion to polyethylene and polypropylene films, which are the most widely used as a base film in the packaging use. Further, the suitability for lamination of these inks, particularly PP direct lamination, is insufficient.
On the other hand, the printing inks that employ a chlorinated polyolefin as a binder exhibit excellent adhesion to polyolefin films but insufficient adhesion to nylon and polyester films and are therefore only applicable to limited kinds of base film. Although this kind of printing ink is suitable for PP direct lamination, it cannot be used in boiling or retort applications and therefore suffers from a limited range of potential uses.
As described above, conventional printing inks have certain problems, that is, the limited range of applicable base films, unsatisfactory adhesion with respect to a wide range of base films despite the possession of general-purpose properties, and a lack of sufficient utility for lamination, and for boiling and retort applications.
Accordingly, the actual practice is to manufacture a printing ink containing a binder which is suitable for both the particular kind of base film to be used and for the processing to be undertaken, e.g., various kinds of lamination and retort processing. Consequently, serious problems have been experienced in the ink manufacturing and, printing processes, as well as in connection with the inventory management of the materials and inks used in these processes.